Magnetic disk devices have made remarkable progress, as external storage devices of computers, owing to their superior of cost/performance ratio and further growth is expected. An aluminum type substrate has been used in the past as a substrate of a magnetic disk which is mounted to the magnetic disk device, but glass substrates, such as chemically tempered glass and crystallized glass, have gradually gained wider application because they have high impact resistance and can be more easily made flat. In other words, the aluminum type substrate can easily provide a magnetic disk having excellent magnetic characteristics but involves the problem of lack of flatness because it can suffer plastic deformation during a mechanical process such as polishing. In contrast, the glass substrate can be easily made flat because it has high surface hardness and does not involve the plastic deformation described above.
Various washing methods have been proposed in the past to sufficiently remove adhering surface matter in a glass substrate production process that laps, polishes and washes the surface of these glass substrates. For example, these methods include a method that processes the glass substrate by a fluorine type solution having pH of 3 to 7 (Japanese Unexamined Patent Publication (Kokai) No. 2000-262991), a method that washes the glass substrate with anodic water obtained by electrolyzing pure water (Japanese Unexamined Patent Publication (Kokai) No. 2001-312817) and a method that washes the glass substrate with a washing solution containing an acid and a reducing agent (Japanese Unexamined Patent Publication (Kokai) No. 2001-206737).